Systems have heretofore been proposed in which a particular type of pattern of registered indications may be detected so as to indicate whether or not a structure under test has particular characteristics. For example, in the Flaherty et al. U.S. Pat. No. 3,673,860, a nondestructive testing system is disclosed in which indications are registered in a shift register matrix and then transferred to a second shift register matrix to which signals are applied to effect scanning, an indicating signal being output when a certain pattern is detected. The system is disclosed as applied to an ultrasonic testing system but it may be used in other types of systems. For example, a similar system is disclosed in the O'Connor et al. U.S. Pat. No. 3,774,030, for use in a magnetic particle inspection system.
Another similar system is disclosed in the Flaherty et al. U.S. Pat. No. 3,774,162 which uses shift registers including large scale integrated circuits and using parallel connections to decoders which are operable to develop serial trains of pulses.
Another type of system is disclosed in the Flaherty et al. U.S. Pat. No. 3,825,820 in which the disclosed nondestructive testing system is an eddy current system operable to develop signals in phase quadrature relation. The indicating system includes a pair of adjustable limit circuits and a pair of comparator circuits operable in a manner such that an indicating signal is output only when the amplitudes of the two signals are simultaneously between set limits. The display arrangement of the disclosed system includes a cathode ray tube in which the deflection of a spot in transverse directions is controlled by the amplitudes of the two signals. The limits set by the limit circuits correspond to a rectangular area or box on the screen of the cathode ray tube and in the system, a box is displayed to indicate such limits.
The Strauts et al. U.S. Pat. No. 4,123,797 discloses an indicating system usable in nondestructive testing applications, as well as in other applications, in which a pair of analog signals are sampled to produce digital numbers which are stored in a memory, the arrangement being such that the memory may be scanned to produce a signal for brightening a scanning spot, the scanning being performed in timed relation to the scanning of a screen. With the system, a pattern may be stored for presentation indefinitely on the screen of a cathode ray tube, but no special storage features are required with respect to the construction of the cathode ray tube.
The systems of such patents are highly advantageous when used in connection with the nondestructive testing systems as disclosed therein as well as in other types of systems. However, such systems have limitations which have not been recognized and dealt with. For example, the systems have had limitations with respect to the type of limits which can be established for determining the type of structural characteristics which will produce an output indication. Also, the circuit arrangements have been more complex than would be desirable and they have had to be specifically constructed for particular types of nondestructive testing systems.